gapi.auth.signOut() signs the current user out of your app.
Learn more.

A new status field indicates whether users are signed in to
Google and/or your website, and a new method field describes how the
sign-in occurred.

You can now specify sign-in parameters once in tags, versus passing
them multiple times to multiple page elements. These page-level
configuration parameters simplify your integration of Google+ Sign-In and
interactive posts Learn
more.

The sign-in callback is now dynamic when using page-level configuration.
This makes it possible, for example, to sync your site’s user experience
across multiple tabs Learn more.

New version (1.3.0) of the iOS
SDK for the Google+ Platform is available. This version simplifies
the integration of Google+ features in iOS apps by adding new framework
files and resource bundles. This update reduces the number of imports
and includes minor bug fixes.

Feb 2013 release - This release includes the following features:

Google+ Sign-In -
Users can sign in to your app with Google on Android, iOS or the web,
using secure authentication. Sign-in enables all of the following features.

Interactive posts -
When a user signs in with Google and shares from your app, their friends
can see a new kind of "interactive" post in their Google+ stream.
Clicking will "deep-link" them to a specific place inside your app to buy,
listen to, or review, for instance.

App Customization -
Once users sign in with Google, they can bring into your app their Google+
public profile, people in their circles, and other Google+ info.
This lets your app welcome them by name, display their picture,
connect them with friends, and lots more. Includes new API:

people.list method -
Lists all of the people who this user has added to one or more circles

App Activities -
When users perform activities within your mobile app such as check-ins,
reviews and commenting on articles, your app can write those activities
to Google. Your app can then make available to the user the type of
activity that best reflects your content or the user's actions.
Includes new API:

Over-The-Air Installs -
After signing in with Google on the web, users have the option, with
a single click on the web, to remotely install your Android app
over-the-air on their mobile device. Linking your web and Android
apps is as simple as registering your project and clients with
the Google Developers Console.

https://www.googleapis.com/auth/plus.login - Allows your app to identify the
authenticated user and retrieve their public profile data, including age range
and preferred language. Includes and expands on
https://www.googleapis.com/auth/plus.me.

Hangouts API - Stable channel, May 2013 -
This version lets apps autoload when Hangouts start, mute the sound for
notifications, and set the broadcast screen of Hangouts On Air to show
or not show the filmstrip.

FEB 2013

Hangouts API v1.4 -
Your app can determine age restrictions, control who is displayed in a
Hangout On Air broadcast, select a primary participant for the main video,
and get the locale of a participant.

OCT 2012

Hangouts API v1.3 -
Your app can control whether the local participant's video is mirrored to the
local participant. A microphone mute function has been renamed.

AUG 2012

Hangouts API v1.2 -
Lets you add sound to a participant’s audio stream that everyone in the
Hangout can hear. A Hangout On Air now defines a broadcaster
and the ability for that broadcaster to control which participants
can be viewed on air. New functions allow for disposing of audio and image
resources from memory. In addition, several general, new functions are
available.

MAY 2012

Hangouts API v1.1 -
Introduces the ability for your app to respond to face movements in real time.
Also provides a new overlay positioned relative to the video feed, new high-rate,
low-latency messages, Hangouts on Air support, the ability to enter any OAuth scope,
and a few other miscellaneous features.

MAR 2012

Hangouts API v1.0 -
Promotes the Hangouts API from developer preview to general release, enabling developers
to launch their hangout apps for sharing by the entire Google+ community.
Multiple overlays can now be visible in a single video feed, and multiple sounds
can now be played at once. Loading of audio and images is now supported not only over
http, but also over https and with data URIs.

FEB 2012

Hangouts API v0.2 -
Introduces the ability to show a video canvas within an app,
adds some general convenience functions, removes some
displayed participant functions in favor of VideoFeed, and removes the
participant highlight functions in favor of setAvatar. Also updates
the Developer Preview hangout user interface to the latest look and feel.

Hangouts API v0.1 first release.
Includes a new location for hangout.js, a major change to the event
pattern, new apis, splits person from participant, moves notice API to
gapi.hangout.layout namespace, and renames APIs.

SEP 2011

Hangouts API
initial Developer Preview release.

HTTP APIs

Formerly known as the REST API.

14, AUG 2013

Aug 2013 release

Google+ Domains API is now available to provide
Google Apps customers and ISVs with an enhanced API that allows for circle
management, writing domain-restricted posts to the stream, and reading posts
and comments that are made by Google Apps domain users.

The access property of each activity has information about
which Community and topic the post has been shared with.
For example,
access.description
can hold the name of the community, such as "Google+ Developers (Discussion)"